Invariants

These are the “don’t break this” rules that keep Untether reliable.

Runner contract

The runner contract is enforced by tests/test_runner_contract.py:

• Exactly one StartedEvent
• Exactly one CompletedEvent
• CompletedEvent is last
• CompletedEvent.resume == StartedEvent.resume

See also the Plugin API runner contract section.

Per-thread serialization

At most one active run may operate on the same thread/session at a time. This is enforced both by scheduling and by per-resume-token runner locks.

Normative details live in the Specification (§5.2).

Resume lines

Resume lines embedded in chat are the engine’s canonical resume command (e.g. claude --resume <id>).

• The runner is authoritative for formatting and extraction.
• Transports/rendering must preserve the resume line reliably (even when trimming/splitting).

Normative details live in the Specification (§3).

Local contribution hygiene

• Run just check before code commits.